Private mail provider DX Mail agreed to date-stamp letters and develop a complaints register in response to ongoing complaints about its Southern District Health Board delivery service.
The board confirmed the changes after releasing information under the Official Information Act that showed it asked DX Mail to take more responsibility for the problem.
Previously, the board tried to play down the extent of the problem, saying in response to queries last month it would like to hear from anyone having issues.
Released minutes from a February meeting between the board and DX Mail concern an agenda item called ''ongoing mail delay complaints''.
The board continued to receive ''generalised complaints'' about mail delivery.
It was difficult to deduce the ''true issues'', and the issue could be caused by changes to New Zealand Post delivery times.
DX Mail, which took over the board's mail service in 2013, uses New Zealand Post's network outside Dunedin, Invercargill and Gore.
The minutes show dealing with the complaints created extra work for health board staff.
The board wanted DX to take a share of the work, such as chasing up details of the complaints.
It wanted DX to date-stamp letters, because otherwise there was ''no visibility'' over when they were processed.
Staff wanted a complaints register because ''having this kind of data would enable us to report more formally back to the DHB on the true nature of the issues''.
A mail delivery time test is set to start this week with 30 health board staff who agreed to participate.
Freightways managing director Dean Bracewell, of Auckland, said DX Mail was ''entirely comfortable'' it was meeting its delivery standard.
The register received only one query since it was established in February.
''During this period, we will have delivered many thousands of letters on behalf of the SDHB.''
DX Mail, which specialises in business mail, is part of Freightways.
